--> Abstract: Paleodepositional Dip Perspective of Fort Union Sandstone Reservoir Architecture, Western Wind River Basin, Wyoming, by R. M. Flores, C. W. Keighin, and W. R. Keefer; #91017 (1992).

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ABSTRACT: Paleodepositional Dip Perspective of Fort Union Sandstone Reservoir Architecture, Western Wind River Basin, Wyoming

FLORES, R. M., C. W. KEIGHIN, and W. R. KEEFER, U.S. Geological Survey, Denver, CO

Muddy Ridge and Pavillion gas fields in the Wind River Indian Reservation produce from fluvial sandstone reservoirs in the lower member of the Paleocene Fort Union Formation. Closely spaced measured sections of this member in the Muddy Creek-Shotgun Bench area, northwest of the gas fields, reveal sandstone architecture within 1-2-mi belts parallel and perpendicular to the northwest-southeast paleodepositional dip. The architecture seen in outcrop reveals more detailed lateral variations of the sandstone reservoirs than can be extrapolated between drill holes, which are 14 mi apart in the nearby gas fields.

Vertical architecture of the sandstone reservoirs changes from combined multistory and isolated fining-upward channel sandstones and conglomeratic sandstones on outcrop to mainly isolated fining-upward channel sandstones at Muddy Ridge and Pavillion fields to

the southeast along paleodepositional dip. The isolated channel sandstones, which represent the major reservoir type in the gas fields, are vertically separated by fine-grained sediments with coarsening-upward sequences of mudstones, siltstones, and sandstones. Lateral architecture in outcrop perpendicular to paleodepositional dip of the multistory sandstone reservoirs are multilateral and broad (<150 ft thick and >1 mi lateral extent). The isolated sandstone reservoirs are multiscoured and narrow (50 ft thick and <0.5 mi lateral extent). In outcrop along paleodepositional dip, these multilateral and isolated sandstone reservoirs are just as thick, but are more laterally extensive. However, they cannot be individually traced along paleodepositional dip between drill holes tow rd and within the Muddy Ridge and Pavillion gas fields.

Rapid variation in reservoir architecture from outcrops to the gas fields reflects a pronounced change in channel patterns from braided (multistory) to meandering (isolated) (with crevasse splay complexes) in an alluvial plain. Thus, small gas fields, such as Muddy Ridge and Pavillion, may be better evaluated by understanding changes in reservoir characteristics that developed in response to paleodepositional-dip fluvial processes.

 

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)